This study will map certain dimensional aspects of personality (impulsivity, anxiety-proneness, and sensation seeking) and laboratory measures of nervous system sensitivity in 200 heterogeneous, clinically and school referred attention deficit disordered (ADD) subjects (structured interview diagnosis) and 50 controls. Behavioral and physiological measures will be obtained during augmentation-reduction and signal detection procedures. The primary goal is to construct a decision tree that will enhance the DSM-III diagnosis of ADD subjects in the sense of making it more predictive of clinical outcome at follow-up. Past research of ours and others indicates that an augmentation-reduction procedure, in which the individual responds to tones of increasing intensity, differentiates hyperactive ADD children from controls and is predictive of therapeutic drug dose. We will attempt to replicate and extend these results using signal detection techniques which would appear to be superior to augmenting procedures for purposes of studying nervous system sensitivity and attentional processes. Russian investigators refer to sensitivity as strength. This is assessed by them as a subject's ability to detect stimuli low in intensity and/or to withstand strong stimuli. We extend this definition to include four hypothesized relatively independent dimensions: sensitivity to tones low and high in intensity and sensitivity to reward and punishment. These four laboratory measures will be correlated with dimensional aspects of personality, including impulsivity, aggressivity, anxiety-proneness, and sensation seeking. Subjects will be grouped post hoc in several ways: (a) on the basis of DSM-III diagnosis; (b) on the basis of DSM-III and personality attributes; (c) on the basis of DSM-III diagnoses and sensitivity indices; and (d) on the basis of DSM-III, personality, and sensitivity measures. We hypothesize that (b), (c) and (d) will be more predictive of clinical outcome than (a). We also expect (b) to correlate more closely with the laboratory measures of sensitivity than (a), but expect (b) and (c) to be independent predictors of outcome and to correlate about equally with outcome. And we expect (d) to be the best predictor of outcome, particularly for children receiving methylphenidate.